Since 2 ATP are used to convert glucose to glyceraldehyde 3-phosphate in glycolysis, can plants bypass this step of ATP investment since they produce glyceraldehyde 3-phosphate directly from the Calvin cycle?

If yes, what would be the final yield of ATP.

If not, why not?

  • Plants produce ATP in the ‘light reaction’ of photosynthesis.

  • The purpose of the Calvin cycle (the ‘dark reactions’) is to produce glucose, for which it uses some of this ATP to provide the energy to make carbon–carbon bonds.

  • Glycolyis in plants functions to produce ATP from reserve carbohydrate etc. when ATP is not available from photosynthesis, or in tissues, that do not have sufficient ATP from photosynthesis.

So this question makes no physiological sense†, as it is based on a misunderstanding of the purposes of the differ metabolic reactions in plants. The answer is not that it cannot happen, but that it would not happen — the regulatory mechanisms that prevent futile cycling of pathways would come into operation.

† It is analogous to saying that the liver can perform gluconeogenesis, and so can produce glyceraldehyde 3-phosphate. So can the liver bypass this step...

  • $\begingroup$ Isn't the dark reaction of photosynthesis the Calvin cycle? From my understanding, the Calvin cycle uses most if not all the atp produced from the light dependent reaction to fix phosphate and reduction of PGA to G3P, which is the final product of the Calvin cycle $\endgroup$ – user35897 May 1 '18 at 16:33
  • $\begingroup$ @user35897 — whoops! Too busy thinking about the structure to get the detail right. Thanks for pointing this out. $\endgroup$ – David May 1 '18 at 16:47

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